Tourmaline

A silicate mineral of very complex chemical composition with isomorphous replacement. Tourmaline occurs in many colours and is a very popular gem.

Tourmaline shop

Origin of name: from the Singhalese word turamali, which means "stone of mixed colour". However, in Sri Lanka this name was used other gemstones as well, e.g. for Zircon.

Synonyms and trade names: apart from the scientific names for Tourmaline species there is a plethora of trade names for differently coloured varieties. The most common names are Rubellite for pink and red Tourmalines, Verdelite for greens and Indigolite for blue stones. Green Tourmaline discs with a red rim are commonly called Watermelon Tourmaline.

Rubellith Turmalin Rubellite TourmalineRubellith Turmalin Rubellite TourmalineRubellith Turmalin Rubellite Tourmaline
Rubellites from Brazil, Pakistan and Nigeria

Verdelith Turmalin Verdelite TourmalineVerdelith Turmalin Verdelite Tourmaline
Verdelites from Africa and Brazil

Chrome Tourmalines are a specialty amongst the Verdelites. They only occur in East Africa and owe their attractive colour to traces of chromium and vanadium.

chromturmalin chrome tourmalinechromturmalin chrome tourmaline
Chrome Tourmalines from Tanzania

Indigolith Turmalin Indigolite TourmalineIndigolith Turmalin Indigolite TourmalineIndigolith Turmalin Indigolite Tourmaline
Indigolite from Namibia

wassermelonenturmalin water melon tourmalineTurmalinscheibe tourmaline discTurmalinscheibe tourmaline disc
A Watermelon Tourmaline from Brazil and
2 Tourmaline discs from Madagascar and Pakistan

For some time the so-called Paraïba Tourmalines were discussed controversially.
In 1989 exceptionally vivid Tourmalines were discovered in the Brazilian federal state of Paraïba. From a mineralogical viewpoint they belonged to the Tourmaline species of Elbaїte, albeit (pardon the pun) with a copper content of up to 2.3%, which is responsible for the exciting colours of these gems.


Paraïba-type Tourmalines.

Paraïba Turmalin TourmalineParaïba Turmalin TourmalineParaïba Typus Turmalin Tourmaline

2 Paraïba Tourmalines and a Paraïba-type Tourmaline from Moçambique (right)

Achroit turmalin achroite tourmaline
Colourless Tourmaline is called Achroite

Multicoloured Tourmalines are common. Fine specimens of intense colour and with clear divisions command high prices amongst connoisseurs.

multicolour tourmaline mehrfärbiger turmalinmulticolour tourmaline mehrfärbiger turmalin paraiba
A tri-colour Tourmaline of selected quality and a very rare bi-coloured Paraïba cabochon

Tourmaline cat's eyes in green and pink are also common.
turmalin katzenauge cat's eye tourmaline

Can be confused with: Tourmaline occurs in all colours and can be confused with many other gems. However, due to it's optical and physical properties, like strong pleochroism and strong birefringence, identification is usually straightforward.

Localities: Tourmaline is found on all continents. Mindat.org lists more than 8600 locations.

Handling: Tourmaline is easy to work with. Do note that many Tourmalines are heat treated at comparatively low temperatures of 450 to 600°C and thus should be protected from high temperatures during repair, to avoid unwanted colour change.

Worth knowing: Tourmalines are piezo-electric. Perportedly Dutch sailors - the Dutch were amongst the first to import Tourmalines into Europe from what today is Sri Lanka - used Tourmaline crystals as Aschetrekker (ash pullers) to remove ash from their smoking pipes.

Tourmaline shop

Gemmological Properties of Tourmaline

Formula:

Tourmaline chemistry is very complex due to isomorphous replacement. The general structural formula is

XY3Z6[(BO3)3T6O18(OH,O)3(OH,F,O)]

X = (Ca,Na,K)
Y = (Mg,Li,Al,Mn,Fe2+,Fe3+,V,Cr,Ti,Cu)
Z = (Al,Mg,Cr,V,Fe3+,Ti)
T = (Si,Al,B,Be)
Crystal system:
trigonal
Mohs hardness:
7-7.5
Specific gravity:
2.85 to 3.35
Refractive index:
1.614 - 1.666
Max. Birefringence:
0.014 to 0.040
Dispersion:
0.017
Pleochroism:
distinct to strong
Luminiscence:
mostly inert
Lustre:
vitreous
Cleavage:
none to indistinct
Fracture:
conchoidal to subconchoidal
Colour:
all